Configure Summary and Floating Static Routes

Configure IPv4 Summary Routes

Summarizing networks into a single address and mask can be done in three steps:

Step 1. List the networks in binary format. Figure 1 lists networks 172.20.0.0/16 to 172.23.0.0/16 in binary format.

Step 2. Count the number of far-left matching bits to determine the mask for the summary route. Figure 2 highlights the 14 far left matching bits. This is the prefix, or subnet mask, for the summarized route: /14 or 255.252.0.0.

Step 3. Copy the matching bits and then add zero bits to determine the summarized network address. Figure 3 shows that the matching bits with zeros at the end results in the network address 172.20.0.0. The four networks - 172.20.0.0/16, 172.21.0.0/16, 172.22.0.0/16, and 172.23.0.0/16 - can be summarized into the single network address and prefix 172.20.0.0/14.

Figure 4 displays R1 configured with a summary static route to reach networks 172.20.0.0/16 to 172.23.0.0/16.